Hektor Johan, Hall Stephen A, Henningsson N Axel, Engqvist Jonas, Ristinmaa Matti, Lenrick Filip, Wright Jonathan P
Division of Solid Mechanics, Lund University, Box 118, 221 00 Lund, Sweden.
Production and Materials Engineering, Lund University, Box 118, 221 00 Lund, Sweden.
Materials (Basel). 2019 Jan 31;12(3):446. doi: 10.3390/ma12030446.
The 3D microstructure around a tin whisker, and its evolution during heat treatment were studied using scanning 3DXRD. The shape of each grain in the sample was reconstructed using a filtered-back-projection algorithm. The local lattice parameters and grain orientations could then be refined, using forward modelling of the diffraction data, with a spatial resolution of 250 n m . It was found that the tin coating had a texture where grains were oriented such that their -axes were predominantly parallel to the sample surface. Grains with other orientations were consumed by grain growth during the heat treatment. Most of the grain boundaries were found to have misorientations larger than 15 ∘ , and many coincidence site lattice (CSL) or other types of low-energy grain boundaries were identified. None of the grains with CSL grain boundaries were consumed by grain growth. During the heat treatment, growth of preexisting Cu6Sn5 occurred; these grains were indexed as a hexagonal η phase, which is usually documented to be stable only at temperatures exceeding 186 ∘ C . This indicates that the η phase can exist in a metastable state for long periods. The tin coating was found to be under compressive hydrostatic stress, with a negative gradient in hydrostatic stress extending outwards from the root of the whisker. Negative stress gradients are generally believed to play an essential role in providing the driving force for diffusion of material to the whisker root.
利用扫描3DXRD研究了锡须周围的三维微观结构及其在热处理过程中的演变。使用滤波反投影算法重建了样品中每个晶粒的形状。然后，利用衍射数据的正向建模，以250nm的空间分辨率细化局部晶格参数和晶粒取向。研究发现，锡涂层具有一种织构，其中晶粒的取向使得它们的轴主要平行于样品表面。在热处理过程中，其他取向的晶粒因晶粒生长而被消耗。发现大多数晶界的取向差大于15°，并识别出许多重合位置点阵（CSL）或其他类型的低能晶界。具有CSL晶界的晶粒均未因晶粒生长而被消耗。在热处理过程中，预先存在的Cu6Sn5发生了生长；这些晶粒被索引为六方η相，通常记录表明该相仅在超过186°C的温度下才稳定。这表明η相可以长期处于亚稳态。发现锡涂层处于静水压力下，静水压力的负梯度从晶须根部向外延伸。一般认为负应力梯度在为材料向晶须根部扩散提供驱动力方面起着至关重要的作用。
